Afc for parametric amplifiers and radars



June 18, 1968 c. VERGNOLLE 3,389,342

AFC FOR PARAME'IRIC AMPLIFIERS AND RADARS Original Filed Oct. 1, 1963 2Sheets-Sheet 1 f4 i 5 f2 0 7"- Qt 1 c F/GJ June 18, 1968 Q VERGNOLLE3,389,342

AFC FOR PARAME'IRIC AMPLIFIERS AND RADARS Original Filed 001;. 1, 1965 2Sheets-Sheet Z V FL 05 106 f Hp I /IOO United States Patent 3,389,342AFC FOR PARAMETRIC AMPLIFIERS AND RADARS Claude Vergnoiie, Paris,France, assignor to CSF-Cornpagnie Generale de Telegraphic ans Fl], acorporation of France Continuation of application Ser. No. 313,037, Oct.1,

1963. This application Sept. 25, 1967, Ser. No. 670,461

Claims priority, applicationgFrance, Oct. 2, 1962,

9 ,01 6 Claims. (Cl. 339-4.5)

ABSTRACT OF THE DISCLOSURE System for receiving ultra-high frequencysignals having a variable carrier frequency and comprising at least oneparametric amplifier whose pumping frequency is controlled by acomputing device. The frequency control is designed in such a mannerthat the conversion gain of the parametric amplifier remains as high aspossible throughout the received band of frequencies.

This application is a continuation of my copending application Ser. No.313,037, filed Oct. 1, 1963, now abancloned.

The present invention relates to parametric amplifiers.

Such amplifiers have the major advantage of amplifying a signal withoutintroducing excessive noise of their own. However, high gain and lownoise figure are obtained only by using circuits with a high Q-factor.As a result, with a fixed pump frequency, any variation of the signalfrequency takes the operation outside its optimum conditions andconsequently causes a decrease of the signaltonoise ratio and reducesthe gain.

It is an object of the present invention to provide a parametricamplifier which provides a high gain and a high signal-to-noise ratio,and yet is tunable over a wide frequency band.

The parametric amplifier according to the invention is characterized inthat, the signal frequency being variable, means are provided forrelating the pump frequency, which is no longer fixed, to the signalfrequency.

The invention will be better understood from the following descriptionand appended drawings, wherein:

FIG. 1 is a circuit diagram of a known parametric amplifier;

FIG. 2 shows a first embodiment of the invention; and

FIGS. 3, 4 and 5 are modifications of the invention.

The same reference numbers designate the same elements throughout allthe figures.

FIG. 1 shows the circuit diagram of a parametric amplifier. Suchamplifiers include a non-linear element C which varies at the pumpfrequency f =F +Af This element couples the input circuit of the signalof frequency f, and the idler frequency circuit, the frequency of theidler signal being f lZf ilTlf These two circuits are tuned to thecentral frequencies of the frequency ranges concerned, namely ),=F \fand f,=F,:Af,. To simplify the description, they will be characterizedby their respective Q-factors Q and Q According to the invention, 1,being variable, f is also variable, and the conditions of this variationwill be stated, setting:

The non-linear element will be, for example, a capacity which variesunder the action of the pump and can be written:

3,389,342 Patented June 18, 1968 ice C=C +AC cos (lvt-f -t) A non-linearinductance or resistance can be used just as well; for example, aferrite, an Esaky diode near its tunnel current, or at its peak current,can be used.

Calculations will be set out for the most useful case in J, is madeequal to f f but the principle would be the same for circuits known inthe technique as up converters.

It is known that the gain of the parametric amplifiers +(Qs s Qi i) +(Q.,Qr r) These formulae show that the gain is high when a is close tounity, and when:

Qs s' Ql i This relation can also be written:

ft! Qs i 1 M M. Q.F.

It is seen from this relation that a fixed pump frequency (Af =0)prevents a maximum conversion gain when A varies; for this to be thecase, Af /Af has to be greater than 1.

A parametric amplifier according to the invention has its pump frequencyrelated to the signal frequency by relation (4).

FIG. 2 shows a first embodiment of the invention.

In this figure a parametric amplifier 1 receives from an antenna 2 asignal at frequency through a cir-culator 3, and delivers at its ouput11, the idler frequency signal f,, or at its output 12, an amplifiedsignal which is delivered to the receiver (not shown) by circulator 2.

The parametric amplifier 1 receives the pump frequency f from a pumposcillator 4. The latters frequency is not fixed, as in known parametricamplifiers. It may be a Carcinotron tube, or any other electronicallytuned tube which receives a control voltage from an amplifier 5, whichin turn, receives its input voltage from a computer 6.

Computer 6 has its input 61 connected to the output of the parametricamplifier through a wavemeter 14 and receives a voltage proportional tof,. Computer 6 then computes the voltage to be applied through device 5to oscillator 4, so that frequency f should satisfy relation (4) for allvariations of the signal frequency i In the case of a receiver of theradar type, the input 61 of the computer can be connected to the radarpilot oscillator, supplying frequency f,.

It may be useful to make the Q-factor Q very large as compared to theQ-factor Q of the signal circuit.

In the case relation (4) becomes:

mixer 8 which receives frequency f,, through a directional coupler 7,connected to the output of circulator 3. It also receives frequency ffrom another directional coupler 9 connected to the output of pumposcillator 4.

The difference f f obtained at the output of mixer controls a voltagegenerator which in turn controls oscillator 4. The pump frequency f iscontrolled by the frequency of the signal.

FIG. 4 is a modification of FIG. 3. Frequency t} .is compared, by meansof a mixer 14, with a fixed reference frequence F supplied by agenerator 15. A control voltage derived from the frequency difference Ff} controls the voltage which in turn controls pump 4.

FIG. 5 shows a further modification.

The arrangement of FIG. 5 is based on the following property valid onlyin the case of negative resistance parametric amplifiers. Suchparametric amplifiers can start oscillating when their gain becomesinfinite, i.e. when the denominator of Formula 2 becomes zero, i.e.when:

t1: 1 and sQs lQl In other words, it will oscillate under the action ofa pump frequency f at frequencies i and f; related to I}, by relation(4).

All that is required is to use sufficient pump power so that nc l.

The arrangement of FIG. 5 is of the radar type using this property.

It includes a pump oscillator 100, supplying a pump signal at frequencyf to a parametric amplifier 101 and this signal has a sufficiently highlevel to ensure that amplifier 101 starts oscillating. It w ll oscillateat frequency f related to f by relation (4). Oscillator 101 thencontrols the transmitter 102 which transmits on frequency f,. Power isradiated by antenna 104. Transmitter 102 is pulse modulated by amodulator 103.

The frequency of oscillator is controlled by a generator 106 which iscontrolled by a device 105.

At the receiver end, the radar includes a parametric amplifier 110,identical to amplifier 101 and also receiving pumping energy at the pumpfrequency f The power level at frequency f received by amplifier 110. isinsufficient to cause it to oscillate, but provides the required gain.

Amplifier 110 receives by antenna 114 and circulator 115 the powerreflected by any object at frequency i in response to the radar pulse ff and f being related, through this arrangement, by relation (4).Amplifier 110 will then be at optimum operating conditions.

Of course the invention is not limited to the embodiments shown anddescribed which are given solely by way of example.

What is claimed is:

1. A parametric amplifier having a first input for receiving a signal ata first frequency; a second input: and an output; an oscillatorfurnishing a signal at a pumping frequency, connected to said secondinput, and having a control input for varying said pumping frequency;and means, controlled by said signal frequency, connected to saidcontrol input for varying said pumping frequency.

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2. A receiver for ultra-high-frequency signals comprising incombination: a parametric amplifier having a first input for receiving asignal at a first frequency; a second input; and an output; anoscillator furnishing a signal at a pumping frequency, connected to saidsecond input, and having a control input for varying said pumpingfrequency; a wavemeter for delivering a first voltage proportional tosaid signal frequency; computing means for receiving said first voltage,and for delivering an output control voltage; and means for deliveringsaid control voltage to said oscillator control input.

5. A receiver for receiving ultrahigh frequency signals, comprising incombination: a parametric amplifier having a first input circuitresonant to the input signal frequency; a second input; an outputcircuit resonant to an idler frequency, the Q factor of said first inputcircuit being negligible with respect to the Q factor of said outputcircuit; a local oscillator, having a frequency control input forgenerating a pumping frequency; and means for locking said pumpingfrequency on said input signal frequency.

4. A receiver for receiving ultra-high frequency signals, comprising incombination: a parametric amplifier having a first input circuit,resonant t0 the input signal frequency; a second circuit; an outputcircuit resonant to an idler frequency, the Q factor of said first inputcircuit being negligible with respect to the Q factor of said output crcuit; a local oscillator having a frequency control input forgenerating a pumping frequency; a mixer having first and second inputsfor receiving said input signal and said pumping frequency respectivelyand an output; means for connecting said output to said frequencycontrol input of said oscillator.

5. A receiver for receiving ultra-high frequency signals, comprising incombination: a parametric amplifier; having a first input circuitresonant to the input signal frequency; a second input circuit; anoutput circuit resonant to an idler frequency, the Q factor of saidfirst input circuit being negligible with respect to the Q factor ofsaid output circuit; a local oscillator having a frequency control inputfor generating a pumping frequency; a mixer for receiving said pumpingfrequency and a stabilized frequency, and delivering an output; meansfor deriving from said output an error control voltage and means forapplying said error voltage to said control input of said oscillator.

6. A receiver for ultra-high frequency signals comprising incombination: a parametric amplifier as claimed in claim 1. wherein saidfrequency varying means comprise: a further parametric amplifieridentical to said parametric amplifier and tuning means; said furtheramplifier having an input coupled to said pumping oscillator and anoutput supplying an oscillatory signal; said tuning means being coupledto said control input for maintaining said oscillatory signal atsynchronism with said received signal.

No references cited.

ROY LAKE, Primary Examiner.

D. R. HOSTETTER, Examiner.

